Creating an Earth System:
Niņo is the result of an on-going "dialog" between the ocean and
atmosphere in the tropical Pacific Ocean. It's part of a natural,
combined oceanic-atmospheric cycle referred to as El Nino-Southern
"Normal" Patterns in the Pacific
1. In normal years when there is no El Niņo or La Niņa, atmospheric
pressure is greater in the eastern Pacific than in the western
Pacific. Because wind flows from higher to lower pressure,
the trade winds blow from east to west.
2. Warm water "piles up" in the western Pacific and sea level
is higher (by ~ 30 cm) than it is in the east.
3. Upwelling of cold, nutrient-rich water occurs
along the western coast of South America.
||4. In some years, this pattern intensifies, so that sea-surface
temperatures are colder than usual in the central and western
Pacific. This condition is referred to as La Niņa
and is similar to normal patterns, except that circulation is
increased and convection is enhanced over Indonesia.
The Southern Oscillation (S0) is an irregular "see-saw"
in which atmospheric pressure and wind patterns shift across the
Pacific. When normally high pressure in the eastern Pacific decreases
and normally low pressure over Australia and northern Indonesia
rises, conditions are right for an El Niņo event to develop.
As warm water shifts eastward, so do the convection and heavy rains
caused by the increased buoyancy of air warmed by the underlying
water. As warm water piles up in the east, upwelling of cold, nutrient-rich
water is inhibited.
Latent heat of condensation further warms the air,
which further decreases atmospheric pressure in the east, etc. The
thunderstorms that have shifted from the western to the central
and eastern Pacific disrupt high-level jet stream
circulation by pumping warm air and moisture high into the atmosphere.
This has a far-reaching effect on weather patterns.
Although El Niņo (and La Niņa) are generated in the tropical Pacific,
their effects are felt all over the world. The process by which
Earth system events in one location are related to events in a different
part of the world is called teleconnections.
- Because each El Niņo event is different, their effects vary.
- At temperate latitudes, the effects show up most clearly during
- Heavy rains on islands of Pacific and the west coast of South
- Drought in Australia, Indonesia, and the Philippines
- Warmer-than-normal winters in northern US and Canada
- Drought in Africa and India
- Weakening of Atlantic hurricanes
- Greater precipitation in SW United States
Impact on California
El Niņo's storm track affects the location of jet streams, which
are a major factor in producing winter weather patterns at mid-latitudes.
Instead of coming ashore in the Pacific Northwest as usual, the
southern jet stream hits California, carrying moisture and storms.
In general, the effect of El Niņo on California is increased rainfall
with accompanying floods, landslides, and coastal erosion. The effects
are variable across the state and are more predictable in Southern
Effects of El Niņo on the Biosphere
- Diminished upwelling of cold, nutrient-rich water upon which
phytoplankton depend. This affects fish, birds, etc.
- Coral bleaching
- Human health: famine, water pollution, diseases such as malaria,
dengue fever, and cholera
All images courtesy of USGS and ENSO (http://www.pmel.noaa.gov)
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